The Democrats are hitting up unions — their go-to cash cows — for last-minute donations to help pay for next month’s convention in Charlotte.

The response from some big unions? Tough.

Union leaders insisted from the start that they wouldn’t help fill the piggy bank for this year’s Democratic National Convention after the party picked a labor-hostile location and at the same time made fundraising tougher by banning corporate contributions and capping individual donations. And with the event less than a month away, they’re sticking to their guns.

Labor unions aren’t slated to sponsor any official convention events, according to a recent convention itinerary obtained by POLITICO. Unions are also refusing to put up the money to back get-out-the-vote efforts they’ve funded in the past.

Heavy hitters like the AFL-CIO, the International Brotherhood of Teamsters, Laborers’ International Union of North America and the International Brotherhood of Electrical Workers say they won’t be making big money contributions this year.

Other unions are toning down their convention involvement with many opting to send a few staffers to engage with union delegates. And some, like the International Association of Machinists and Aerospace Workers, have said they are sitting out entirely.

“[T]here was a general disappointment in the selection because of the non-union hotels, the non-union accommodations in North Carolina,” said Chuck Rocha, president of the union consulting firm Solidarity Strategies and former political director of the United Steelworkers union.

“I think everybody is on the same page politically around a lot of different candidates, but the unions are going to invest in their members before they invest in a convention that’s being held in a place where there are no organized hotels, organized restaurants, etc.,” Rocha added.

It’s a far cry from 2008, when unions accounted for nearly $9 million of the $62 million raised to fund the Democratic Convention in Denver, according to campaign finance reports. Unions also cut big checks for delegate lunches, rallies and policy events on issues like immigration and housing.

And it’s clear that labor’s money is being missed. While some big unions, such as the Service Employees International Union, are giving, convention organizers were reportedly more than $25 million short of their $36.6 million goal as of late June. Democrats also cut the week shorter by eliminating Labor Day Monday from their schedule, then moved a planned rally and organizing event from the Charlotte Motor Speedway to the streets of uptown Charlotte.

Under the Democrats’ self-imposed fundraising rules, direct corporate contributions are banned and individual gifts are capped at $100,000. That makes unions — which are still allowed to give unlimited amounts from their treasuries — an obvious solution to Democrats’ fundraising gap.

Democratic officials even gave officials from the AFL-CIO, the Teamsters and the United Auto Workers a tour of the convention site in April and party fundraisers have kept up phone calls and meetings to woo labor into giving cash.

But so far, not a single union-sponsored event is listed among the more than 120 that have been pulled together on a convention events list that is circulating among Washington insiders.

“I think that [Democrats] were probably surprised at the pushback knowing that there’s been a longstanding partnership,” Rocha said. “I think there’s some general education that has to go on at different levels of the party to understand the challenges that we face every day in the labor movement.”

Democratic consultant Bruce Kieloch had labor’s help in organizing a high-profile bash to kick off the Denver convention for the get-out-the-vote group HeadCount. But, Kieloch said the unions aren’t participating this time.

“Most of the folks who made that event possible aren’t going,” Kieloch said.

Some labor groups are planning their own rally this week in Philadelphia to focus on labor rights. The Aug. 11 event, dubbed “Workers Stand for America,” has the backing of the International Brotherhood of Electrical Workers, the AFL-CIO and other labor groups.

Some labor groups were incensed by the Democrats’ decision to hold the festivities in North Carolina — a right-to-work state. Others say the decision is part of a broader agenda to focus cash resources on state and local races in which labor has a big stake.

“Having the convention in Charlotte was kind of a wake-up call to that fact that really no one’s paying attention to the middle class and to working people in this country,” Ed Hill, president of the IBEW said last month.

The Laborers’ International Union of North America was the top union donor to the 2008 convention, spending $1.5 million. This time around, it’s not giving at all.

LIUNA spokesman Richard Greer said the group invested in the 2008 convention because it represented a “historic, singular moment in our country’s history” and a “tremendous opportunity for us to raise the profile of our members.”

“We’re in a different time now,” he added. “We think the best resources of our members’ hard-earned contributions are in election outreach and reelecting President Obama.”

The International Brotherhood of Teamsters will invest “significantly less” in Charlotte than it has in past conventions and will send only “limited staff” to support the 17 Teamster delegates attending, said spokesman Galen Munroe. The Teamsters donated $250,000 to the Denver convention.

Munroe declined to give specifics about the reasoning for cutting back on cash, saying only, “It’s just a decision internally right now.” He said the union wasn’t approached by the Democratic Party “other than the initial ask that they made,” but he declined to give a dollar figure.

AFL-CIO President Richard Trumka last month said the federation won’t cut any big checks for the convention, the host committee or events surrounding the convention. “We won’t be buying skyboxes, hosting events other than the labor delegates meeting or bringing a big staff contingent to the convention,” Trumka wrote in a letter to labor officials. The AFL-CIO donated $100,000 for the Denver convention.

Trumka said he would be attending the convention in Charlotte, however, to lead the delegates’ meeting and “to convey labor’s coordinated message where appropriate.”

Democrats have tried to smooth things over with labor groups frustrated by the Obama administration’s limited agenda on their issues. Since then, Obama has made major overtures to the labor movement, backing a union-supported jobs package and making three recess appointments to the National Labor Relations Board, which is charged with enforcing the right of private-sector employees to organize and form unions.

Convention organizers say they’re already getting help — including financial support — from many labor groups.

“We are pleased with the broad support we have from organized labor to help make this year’s convention the most open and accessible convention in history,” said Democratic National Committee spokeswoman Melanie Roussel.

Convention officials declined to say how much of their cash has come from unions so far. But some unions are sending cash, and a convention official said labor groups are participating in various forms beyond financial contributions, such as sending delegates and special guests and hosting briefings, trainings, meetings and receptions in Charlotte.

The National Education Association gave $1.2 million to Charlotte organizers , although it hasn’t publicly detailed its convention plans.

The Service Employees International Union, which donated $1.4 million to event organizers in 2008, is already spending on the Charlotte event, although SEIU spokesman Mark McCullough wouldn’t say how much.

“We’re certainly against North Carolina’s right-to-work-for-less status and anti-working families status, but I just think that there’s a number of different places where different unions come down on this,” McCullough said.

By withholding cash — as event organizers face a funding shortfall — major unions are defying the notion that they’ll shell out big whenever national Democrats come calling.

One Democratic lobbyist said the reason unions aren’t reacting to the arm twisting is that the Democratic National Committee and the Obama administration haven’t laid the foundation for a good relationship.

“One of the greatest frustrations with this administration is how they treat members and everyone else. It’s sort of this attitude that they’ll come because they are Democrats,” the lobbyist said.